[Q] hardware buttons not working

I bought a new sensation mobo. I ripped it from a faulty phone I bought. The hardware touch buttons on the bottom don't work. I've swapped around other internal parts from other older sensation phones I have but they still won't work. I've swapped around the digitizer and other parts. I can't figure which part need to be replaced. Could it be it's the mobo itself that's faulty. I'm using software keys in the meantime till I figure it out but not as good as I get a smaller usable screensize. I don't think it has anything to do with the sofware either as I've used a few custom roms on it. Any ideas anyone ?

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